(function (root, definition) {
    'use strict';
    if (typeof define === 'function' && define.amd) {
        define(definition);
    } else if (typeof module === 'object' && module.exports) {
        module.exports = definition();
    } else {
        root.log = definition();
    }
})(this, function () {
    'use strict';

    var has = Object.prototype.hasOwnProperty,
        prefix = '~';

    /**
     * Constructor to create a storage for our `EE` objects.
     * An `Events` instance is a plain object whose properties are event names.
     *
     * @constructor
     * @private
     */
    function Events() {}

    //
    // We try to not inherit from `Object.prototype`. In some engines creating an
    // instance in this way is faster than calling `Object.create(null)` directly.
    // If `Object.create(null)` is not supported we prefix the event names with a
    // character to make sure that the built-in object properties are not
    // overridden or used as an attack vector.
    //
    if (Object.create) {
        Events.prototype = Object.create(null);

        //
        // This hack is needed because the `__proto__` property is still inherited in
        // some old browsers like Android 4, iPhone 5.1, Opera 11 and Safari 5.
        //
        if (!new Events().__proto__) prefix = false;
    }

    /**
     * Representation of a single event listener.
     *
     * @param {Function} fn The listener function.
     * @param {*} context The context to invoke the listener with.
     * @param {Boolean} [once=false] Specify if the listener is a one-time listener.
     * @constructor
     * @private
     */
    function EE(fn, context, once) {
        this.fn = fn;
        this.context = context;
        this.once = once || false;
    }

    /**
     * Add a listener for a given event.
     *
     * @param {EventEmitter} emitter Reference to the `EventEmitter` instance.
     * @param {(String|Symbol)} event The event name.
     * @param {Function} fn The listener function.
     * @param {*} context The context to invoke the listener with.
     * @param {Boolean} once Specify if the listener is a one-time listener.
     * @returns {EventEmitter}
     * @private
     */
    function addListener(emitter, event, fn, context, once) {
        if (typeof fn !== 'function') {
            throw new TypeError('The listener must be a function');
        }

        var listener = new EE(fn, context || emitter, once),
            evt = prefix ? prefix + event : event;

        if (!emitter._events[evt])
            (emitter._events[evt] = listener), emitter._eventsCount++;
        else if (!emitter._events[evt].fn) emitter._events[evt].push(listener);
        else emitter._events[evt] = [emitter._events[evt], listener];

        return emitter;
    }

    /**
     * Clear event by name.
     *
     * @param {EventEmitter} emitter Reference to the `EventEmitter` instance.
     * @param {(String|Symbol)} evt The Event name.
     * @private
     */
    function clearEvent(emitter, evt) {
        if (--emitter._eventsCount === 0) emitter._events = new Events();
        else delete emitter._events[evt];
    }

    /**
     * Minimal `EventEmitter` interface that is molded against the Node.js
     * `EventEmitter` interface.
     *
     * @constructor
     * @public
     */
    function EventEmitter() {
        this._events = new Events();
        this._eventsCount = 0;
    }

    /**
     * Return an array listing the events for which the emitter has registered
     * listeners.
     *
     * @returns {Array}
     * @public
     */
    EventEmitter.prototype.eventNames = function eventNames() {
        var names = [],
            events,
            name;

        if (this._eventsCount === 0) return names;

        for (name in (events = this._events)) {
            if (has.call(events, name)) names.push(prefix ? name.slice(1) : name);
        }

        if (Object.getOwnPropertySymbols) {
            return names.concat(Object.getOwnPropertySymbols(events));
        }

        return names;
    };

    /**
     * Return the listeners registered for a given event.
     *
     * @param {(String|Symbol)} event The event name.
     * @returns {Array} The registered listeners.
     * @public
     */
    EventEmitter.prototype.listeners = function listeners(event) {
        var evt = prefix ? prefix + event : event,
            handlers = this._events[evt];

        if (!handlers) return [];
        if (handlers.fn) return [handlers.fn];

        for (var i = 0, l = handlers.length, ee = new Array(l); i < l; i++) {
            ee[i] = handlers[i].fn;
        }

        return ee;
    };

    /**
     * Return the number of listeners listening to a given event.
     *
     * @param {(String|Symbol)} event The event name.
     * @returns {Number} The number of listeners.
     * @public
     */
    EventEmitter.prototype.listenerCount = function listenerCount(event) {
        var evt = prefix ? prefix + event : event,
            listeners = this._events[evt];

        if (!listeners) return 0;
        if (listeners.fn) return 1;
        return listeners.length;
    };

    /**
     * Calls each of the listeners registered for a given event.
     *
     * @param {(String|Symbol)} event The event name.
     * @returns {Boolean} `true` if the event had listeners, else `false`.
     * @public
     */
    EventEmitter.prototype.emit = function emit(event, a1, a2, a3, a4, a5) {
        var evt = prefix ? prefix + event : event;

        if (!this._events[evt]) return false;

        var listeners = this._events[evt],
            len = arguments.length,
            args,
            i;

        if (listeners.fn) {
            if (listeners.once) this.removeListener(event, listeners.fn, undefined, true);

            switch (len) {
                case 1:
                    return listeners.fn.call(listeners.context), true;
                case 2:
                    return listeners.fn.call(listeners.context, a1), true;
                case 3:
                    return listeners.fn.call(listeners.context, a1, a2), true;
                case 4:
                    return listeners.fn.call(listeners.context, a1, a2, a3), true;
                case 5:
                    return listeners.fn.call(listeners.context, a1, a2, a3, a4), true;
                case 6:
                    return listeners.fn.call(listeners.context, a1, a2, a3, a4, a5), true;
            }

            for (i = 1, args = new Array(len - 1); i < len; i++) {
                args[i - 1] = arguments[i];
            }

            listeners.fn.apply(listeners.context, args);
        } else {
            var length = listeners.length,
                j;

            for (i = 0; i < length; i++) {
                if (listeners[i].once)
                    this.removeListener(event, listeners[i].fn, undefined, true);

                switch (len) {
                    case 1:
                        listeners[i].fn.call(listeners[i].context);
                        break;
                    case 2:
                        listeners[i].fn.call(listeners[i].context, a1);
                        break;
                    case 3:
                        listeners[i].fn.call(listeners[i].context, a1, a2);
                        break;
                    case 4:
                        listeners[i].fn.call(listeners[i].context, a1, a2, a3);
                        break;
                    default:
                        if (!args)
                            for (j = 1, args = new Array(len - 1); j < len; j++) {
                                args[j - 1] = arguments[j];
                            }

                        listeners[i].fn.apply(listeners[i].context, args);
                }
            }
        }

        return true;
    };

    /**
     * Add a listener for a given event.
     *
     * @param {(String|Symbol)} event The event name.
     * @param {Function} fn The listener function.
     * @param {*} [context=this] The context to invoke the listener with.
     * @returns {EventEmitter} `this`.
     * @public
     */
    EventEmitter.prototype.on = function on(event, fn, context) {
        return addListener(this, event, fn, context, false);
    };

    /**
     * Add a one-time listener for a given event.
     *
     * @param {(String|Symbol)} event The event name.
     * @param {Function} fn The listener function.
     * @param {*} [context=this] The context to invoke the listener with.
     * @returns {EventEmitter} `this`.
     * @public
     */
    EventEmitter.prototype.once = function once(event, fn, context) {
        return addListener(this, event, fn, context, true);
    };

    /**
     * Remove the listeners of a given event.
     *
     * @param {(String|Symbol)} event The event name.
     * @param {Function} fn Only remove the listeners that match this function.
     * @param {*} context Only remove the listeners that have this context.
     * @param {Boolean} once Only remove one-time listeners.
     * @returns {EventEmitter} `this`.
     * @public
     */
    EventEmitter.prototype.removeListener = function removeListener(
        event,
        fn,
        context,
        once
    ) {
        var evt = prefix ? prefix + event : event;

        if (!this._events[evt]) return this;
        if (!fn) {
            clearEvent(this, evt);
            return this;
        }

        var listeners = this._events[evt];

        if (listeners.fn) {
            if (
                listeners.fn === fn &&
                (!once || listeners.once) &&
                (!context || listeners.context === context)
            ) {
                clearEvent(this, evt);
            }
        } else {
            for (var i = 0, events = [], length = listeners.length; i < length; i++) {
                if (
                    listeners[i].fn !== fn ||
                    (once && !listeners[i].once) ||
                    (context && listeners[i].context !== context)
                ) {
                    events.push(listeners[i]);
                }
            }

            //
            // Reset the array, or remove it completely if we have no more listeners.
            //
            if (events.length)
                this._events[evt] = events.length === 1 ? events[0] : events;
            else clearEvent(this, evt);
        }

        return this;
    };

    /**
     * Remove all listeners, or those of the specified event.
     *
     * @param {(String|Symbol)} [event] The event name.
     * @returns {EventEmitter} `this`.
     * @public
     */
    EventEmitter.prototype.removeAllListeners = function removeAllListeners(event) {
        var evt;

        if (event) {
            evt = prefix ? prefix + event : event;
            if (this._events[evt]) clearEvent(this, evt);
        } else {
            this._events = new Events();
            this._eventsCount = 0;
        }

        return this;
    };

    //
    // Alias methods names because people roll like that.
    //
    EventEmitter.prototype.off = EventEmitter.prototype.removeListener;
    EventEmitter.prototype.addListener = EventEmitter.prototype.on;

    //
    // Expose the prefix.
    //
    EventEmitter.prefixed = prefix;

    //
    // Allow `EventEmitter` to be imported as module namespace.
    //
    EventEmitter.EventEmitter = EventEmitter;

    // //
    // // Expose the module.
    // //
    // if ('undefined' !== typeof module) {
    //   module.exports = EventEmitter;
    // }
    // exports.EventEmitter = EventEmitter;
    return EventEmitter;
});
